Screens for downhole use typically are formed around a base pipe that is perforated or has some sort of openings. The base pipe is attached as part of a string extending downhole so that it can be properly positioned in a producing zone. Around the base pipe is a filter material and around the filter material is an outer shroud. The outer shroud is usually a thin metallic tube with punched openings that is designed to protect the screen material from damage when run in or when pulled out of the hole. The louvers are usually sufficiently large so as to not meaningfully restrict flow to the filter material. The target size particle for exclusion is determined by the opening size in the screen material.
In the past the screen material that has seen wide spread use is a Dutch Twill weave as shown and described in U.S. Pat. No. 5,611,399. This patent also shows a technique of running a tubular assembly through a die to close an overlapping longitudinal seam made of ends that are bent and doubled over on the tube shape. Other patents that relate to manufacturing screens for downhole use are U.S. Pat. Nos. 6,305,468 and 6,607,032.
The past techniques had a disadvantage of distinct out of round shape due to the doubling over of ends and folding them over. As a result during the process of joining to the base pipe, the applied compressive force to try to secure the ends of the assembly to the base pipe or to seal a longitudinal or spiral seam were not optimal. This was because the out of round shape limited the ability to uniformly apply a sealing compressive force all around the screen structure without overstressing the built up area of the folded and doubled over material of the filtration media. Another issue was the use of the Dutch Twill weave design from the point of view of cost and bulk when trying to form a seam.
The present invention relates to the use of layers of flat weave mesh material and diffusion bonding the layers to make a cohesive filter layer assembly that gets the performance of Dutch Twill weave at a fraction of the cost. Additionally, the assembly mating edges are compressed to reduce their thickness so that when rolled into a tube shape the ends will overlap and the thickness at the overlapping seam will be approximately the thickness of the assembly elsewhere thus minimizing the out or roundness of the shape and allowing a stronger joint to extend the length of the assembly as well as stronger end connections. Optionally, a resilient material can be placed on the overlapping edges and compressed into the weave either initially, when the assembly is still in flat sheet form, or thereafter when the assembly is in tube form and moved through a die with the base pipe. Those skilled in the art will more readily appreciate the details of the preferred mode of the invention from the description below and the associated drawings while recognizing that the full scope of the invention is to be found in the claims.